The Streptococci make up a medically important genera of microbes known to cause several types of disease in humans, including, for example, otitis media, conjunctivitis, pneumonia, bacteremia, meningitis, sinusitis, pleural empyema and endocarditis, and most particularly meningitis, such as for example infection of cerebrospinal fluid. Since its isolation more than 100 years ago, Streptococcus pneumoniae has been one of the more intensively studied microbes. For example, much of our early understanding that DNA is, in fact, the genetic material was predicated on the work of Griffith and of Avery, Macleod and McCarty using this microbe. Despite the vast amount of research with Streptococcus pneumoniae, many questions concerning the virulence of this microbe remain. It is particularly preferred to employ Streptococcal genes and gene products as targets for the development of antibiotics.
Riboflavin (vitamin B2) is a member of the B complex of vitamins which function as coenzymes in metabolic reactions. Riboflavin has two coenzyme forms, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) which act in oxidation-reduction reactions such as the cytochrome system of electron transport and the oxidative degradation of pyruvate, fatty acids and amino acids. The first committed step in the biosynthesis of riboflavin is the opening of the imidazole ring of GTP. In the presence of 3 H.sub.2 O and Mg.sup.++, the C-8 of GTP is released as formate accompanied by the release of pyrophosphate by the action of GTP cyclohyrolase II (GCH2; EC 3.5.4.25). This enzyme function is encoded by ribA in bacteria and rib1 in yeast species. Through a series of steps, involving 3,4-dihydroxy-2-butanone 4 phosphate synthase (ribA), 6,7-dimethyl-8-ribityllumazine synthase (ribH), riboflavin synthase (ribB), pyrimidine deaminase and pyrimidine reductase (ribG), enzymes encoded by genes within the riboflavin biosynthesis operon, riboflavin is formed. Because GCH2 catalyzes the first committed step in the biosynthesis of riboflavin (Richter G, et al. (1993) Biosynthesis of riboflavin: cloning, sequencing, mapping, and expression of the gene coding for GTP cyclohydrolase II in Escherichia coli. J Bacteriol. 175:4045-4051), is present in many pathogenic microorganisms, and since riboflavin biosynthesis has shown to be required for virulence in the swine pathogen Actinobacillus pleuropneumoniae (Fuller, T E, et al. (1996) A riboflavin auxotroph of Actinobacillus pleuropneumoniae is attenuated in swine. Infect. Immun. 64:4659-4664), it represents a broad spectrum antibacterial as well as antifungal target.
The frequency of Streptococcus pneumoniae infections has risen dramatically in the past few decades. This has been attributed to the emergence of multiply antibiotic resistant strains and an increasing population of people with weakened immune systems. It is no longer uncommon to isolate Streptococcus pneumoniae strains which are resistant to some or all of the standard antibiotics. This phenomenon has created a demand for both new anti-microbial agents, vaccines, and diagnostic tests for this organism.
Clearly, there exists a need for factors, such as the ribA embodiments of the invention, that have a present benefit of being useful to screen compounds for antibiotic activity. Such factors are also useful to determine their role in pathogenesis of infection, dysfunction and disease. There is also a need for identification and characterization of such factors and their antagonists and agonists to find ways to prevent, ameliorate or correct such infection, dysfunction and disease.
Certain of the polypeptides of the invention possess amino acid sequence homology to a known Actinobacillus pleuropneumoniae ribA protein. (Swiss Prot. Accession no. P50855; GenBank Accession no. U27202; Richter, G. et al., J. Bacteriol. 175:4045-4051 (1993); Fuller, T. E. et al., Infect. Immun. 64:4659-4664 (1996); Foor, F. et al., Methods Enzymol. 66:303-307 (1980).)